Switch to PKCS8 encoding of ecdsa private keys to keep it aligned with ed25519...

Switch to PKCS8 encoding of ecdsa private keys to keep it aligned with ed25519 private keys. This fixes ecdsa key handling on Android clients

pkg/api/cert.go

@@ -105,7 +105,7 @@ func (r *registry) CertWriter(ovpnCaCrt string, ovpnCaKey string, algo string, e
 			return "", err
 		}
 		// Write the private key
-		keyBytes, err := x509.MarshalECPrivateKey(priv)
+		keyBytes, err := x509.MarshalPKCS8PrivateKey(priv)
 		if err != nil {
 			return "", err
 		}